1. Field of the Invention
The present invention relates to a colorimetry method of an image output by a copying machine, printer, or the like of an ink-jet system, electrophotography system, or the like.
2. Description of the Related Art
Conventionally, a spectrocolorimeter (color sensor) is used as an apparatus for measuring colors of printed products and objects. The spectrocolorimeter irradiates the object to be measured with white light, and detects, using a line sensor, intensities of dispersing light rays after reflected light is diverged for respective wavelengths using a diffraction grating or prism. Then the spectrocolorimeter calculates spectral reflectances of the object to be measured by making calculations in consideration of a wavelength distribution of the detected dispersing light intensities, that of light of a light source, a spectral sensitivity of the sensor, and the like. In this case, since an amount of light entering the object to be measured is not uniform over the full wavelength range of visible light, the intensities of incident light rays for respective wavelengths are required to be calculated so as to calculate the spectral reflectances of the object to be measured, and the wavelength distribution of light rays entering respective pixels of the line sensor is required to be calculated.
However, the relationship between the respective pixels of the line sensor and wavelengths which are value-set on these pixels deviates due to aging or thermal changes. Note that “value-setting” indicates to associate them with each other. For this reason, in order to correctly measure the wavelength distribution of reflected light and to attain correction based on the intensity distribution of incident light, the wavelengths which are value-set on the respective pixels of the line sensor have to be appropriately calibrated.
To solve the above problem, Japanese Patent Laid-Open No. 2003-114187 has proposed the following method. That is, for a line sensor on which light-receiving elements (pixels) for colorimetry are arranged in a line, pixels of the sensor are arranged to be more than the minimum required number. Furthermore, a filter for absorbing light rays of wavelengths other than visible light is arranged between a spectral optical element and the sensor, or a light-emitting element which emits light of a predetermined wavelength is added, thereby specifying wavelengths of light rays which enter the respective pixels of the sensor. According to this method, since the wavelengths of light rays which enter the respective pixels of the sensor are specified, the need for precise components and strict management and adjustment of positional precision can be obviated, thus allowing detection of the spectral reflectances of toner patches with low cost.
However, the method proposed by Japanese Patent Laid-Open No. 2003-114187 additionally requires light absorbing unit (filter) and is disadvantageous in terms of cost. Alternatively, depending on a filter to be used, visible light is attenuated, thus lowering colorimetry precision.